1. Field of the Invention
This application relates generally to gas turbine engine blades and, more particularly, to methods for welding airfoil sections of gas turbine engine rotor blades.
2. Description of Related Art
At least some known gas turbine engines include a compressor for compressing air which is mixed with a fuel and channeled to a combustor wherein the mixture is ignited within a combustion chamber for generating hot combustion gases. The hot combustion gases are channeled downstream to a turbine, which extracts energy from the combustion gases for powering the compressor, as well as producing useful work to propel an aircraft in flight or to power a load, such as an electrical generator.
Known compressors include a rotor assembly that includes at least one row of circumferentially spaced rotor blades. Each rotor blade includes an airfoil that includes a pressure side, and a suction side extending between leading and trailing edges. Each airfoil extends radially outward from a rotor blade platform, disk, or drum. Some rotor blades also include a dovetail that extends radially inward from a shank coupled to a platform. The dovetail is used to mount the rotor blade to a rotor disk or drum. In at least some known compressors, the rotor blade is formed integrally with the rotor disk or drum and the assembly is often referred to as a BLISK or BLUM. Fan, compressor and other gas turbine engine rotors may have a BLISK or a BLUM. BLISKS have blades that are integral with a disk and BLUMS have blades that are integral with a drum. Conventionally, BLISKS and BLUMS are made by machining an airfoil shape (using conventional machining or ECM/EDM processes) from a forged disk. Linear and angularly reciprocating friction welding methods have been developed for manufacturing BLISKS and BLUMS for gas turbine engine rotors. Angularly reciprocating friction welding includes the disc or drum rotor being angularly reciprocated while the airfoils or blades are pressed radially against the disk or rotor circumference. Linear reciprocating friction welding includes linear reciprocating airfoils or the blades as they are pressed radially against the disk or rotor circumference.
During engine operation, leading and trailing edges of the blade and/or a tip of the compressor blade airfoil may deteriorate or become damaged due to any of a number of distress modes, including, but not limited to, foreign object damage (FOD), tip rubbing, oxidation, thermal fatigue cracking, or erosion caused by abrasives and corrosives in the flowing gas stream. To facilitate mitigating such operational effects, the blades are periodically inspected for damage, and a determination of an amount of damage and/or deterioration is made. If the blades have lost a substantial quantity of material, they are replaced. If the blades have only lost a small quantity material, they may be returned to service without repair. Alternatively, if the blades have lost an intermediate quantity of material, the blade airfoils may be repaired.
For example, at least one known method of repairing a turbine compressor blade airfoil includes mechanically removing, such as by grinding, a worn and/or damaged tip area and then adding a material deposit to the tip to form the tip to a desired dimension. The material deposit may be formed by several processes including welding and/or thermal spraying. Furthermore, special tooling is also used to achieve the precise dimensional relations between the original portion of the compressor blade and the added portion of the compressor blade airfoil. Thus, replacing a portion of a compressor blade airfoil may be a time-consuming and expensive process. Additionally, more complex airfoil shapes, for example three-dimensional aerodynamic configurations may increase the difficulty of welding and blending the repaired airfoil, thus resulting in increased repair costs. Thus, it is highly desirable to reduce the time and expense of replacing or attaching airfoil sections on both blades and BLISKS or BLUMS.